This invention relates to solid propellants, and in particular to bonding agents for polyurethane propellant binders.
Heretofore, it has been proposed to use bonding agents to form a hard and tough binder layer around the filler in a solid propellant, the filler normally being the oxidizing agent. This envelope is linked to the binder matrix by primary chemical bonds. In order to accomplish this result, a bonding agent must fulfill the requirements of being adsorbed to the oxidizer surface and of forming a tough and coherent layer. One known bonding agent is 2,3-dihydroxypropyl-bis(2-cyanoethyl)amine. With this bonding agent, the adsorption is accomplished essentially by its in solubility in the binder phase. In propellant binders where this bonding agent is too soluble, such as nitroplasticized systems, it becomes inefficient. Similarly, the formation of a tough 2,3-dihydroxypropyl-bis(2-cyanoethyl)amine layer depends on the high reactivity of the hydroxyl groups toward the isocyanate, which must be higher than the reactivity of the other alcoholic constituents in the binder matrix. Therefore, in binder systems having very reactive prepolymers, 2,3-dihydroxypropyl-bis(2-dyanoethyl)amine becomes inefficient.
In U.S. Pat. No. 4,000.023, there are disclosed bonding agents which do not depend on hydroxyl groups and the ensuing urethane reaction to yield the envelope necessary for bonding. Also, being strong bases these bonding agents are chemisorbed as well as adsorbed to the surface of the oxidizing agent. These bonding agents have the general formula EQU X.sub.2 N(CH.sub.2 CH.sub.2 NX).sub.n CH.sub.2 CH.sub.2 NX.sub.2
wherein n is an integer having a value of 1 to 12, and X is hydrogen, cyanoethyl, dihydroxypropyl or mixtures thereof with the proviso that at least one X is hydrogen.
In particular, the said patent focused upon tetraethylene pentamine and its cyanoethyl and dihydroxypropyl derivatives.
We have now found that these cyanoethyl-modified bonding agents can be further modified to provide more improved bonding agents.
Accordingly, it is an object of the present invention to provide an improved group of bonding agents for solid rocket propellants having polyurethane binders.
It is another object of this invention to provide a method for making improved bonding agents.
Other objects and advantages of the invention will be apparent from the description which follows.